1. Field of the Invention
The present invention relates generally to radiation therapy devices, and more particularly, to a rotatable multi-element beam shaping device for use in a radiation therapy device.
2. Description of the Related Art
Conventional radiation therapy typically involves directing a radiation beam at a tumor in a patient to deliver a predetermined dose of therapeutic radiation to the tumor according to an established treatment plan. This is typically accomplished using a radiation therapy device such as the device described in U.S. Pat. No. 5,668,847 issued Sep. 16, 1997 to Hernandez, the contents of which are incorporated herein for all purposes.
Tumors have three-dimensional treatment volumes which typically include segments of normal, healthy tissue and organs. Healthy tissue and organs are often in the treatment path of the radiation beam. This complicates treatment, because the healthy tissue and organs must be taken into account when delivering a dose of radiation to the tumor. While there is a need to minimize damage to healthy tissue and organs, there is an equally important need to ensure that the tumor receives an adequately high dose of radiation. Cure rates for many tumors are a sensitive function of the dose they receive. Therefore, it is important to closely match the radiation beam""s shape and effects with the shape and volume of the tumor being treated.
In many radiation therapy devices, the treatment beam is projected through a pre-patient collimating device (a xe2x80x9ccollimatorxe2x80x9d), that defines the treatment beam profile or the treatment volume at the treatment zone. A number of different collimator techniques have been developed to attempt to conform the dose rate and the treatment volume to the shape of the tumor while taking nearby healthy tissue and organs into account. A first technique is to use a collimator with solid jaw blocks positioned along a path of the treatment beam to create a field shape based on the shape of the tumor to be treated. Typically, two sets of blocks are provided, including two blocks making up a Y-jaw generally disposed parallel to a Y-axis (with the Z-axis being parallel to the beam path), and two blocks making up an X-jaw generally disposed parallel to an X-axis. The X-jaw is conventionally placed between the Y-jaws and the patient.
These solid jaw blocks, however, do not provide sufficient variability in the field shape. In particular, where the tumor has a shape which requires a field edge relatively parallel to the edge of the jaw blocks, the edge of the jaw block becomes more predominant in forming the field edge. As a result, undulation of the field increases as well as the effective penumbra. This can be particularly difficult where the treatment beam is an X-ray beam. It is also difficult to adjust the field shape where the treatment beam is an electron beam due to electron attenuation and scattering.
Multileaf, or xe2x80x9cmultielementxe2x80x9d block collimators were developed to provide more variation and control over the shape of the field at the treatment zone. An example multielement collimator is described in U.S. Pat. No. 5,591,983 issued to Hughes on Jan. 7, 1997. The Hughes collimator uses an X-jaw which has two blocks each made up of a number of individual elements. Each of the elements of the X-jaw can be moved longitudinally across the path of the radiation beam to create a desired beam shape at the point of treatment.
Further control over the shape of the beam is desirable. Existing block collimators fix the position of the Y-jaw with respect to the X-jaw, that is, the Y-jaw blocks do not move independently of the X-jaw blocks. As a result, many treatments involve tumors having a shape relatively parallel to one or more edges of either the X- or Y-jaws. Delivery of an appropriate therapeutic dose of radiation to these tumors can be difficult due to radiation scattering, undulation, and penumbra effects.
Therefore, it would be desirable to provide a system and method which allows further control of each of the blocks, each of the jaws, and each of the elements in a multielement collimator to increase control over the beam shape, including control over the penumbra and undulation effects which can arise when the treatment field edge becomes relatively parallel to edges of the blocks, jaws, and/or elements of the collimator. It would also be desirable to provide control over the beam shape to provide more accurate control during treatment to accommodate beam attenuation and scattering.
Pursuant to some embodiments, methods and apparatus for generating a plurality of sets of segment data are provided which include inputting treatment data into a planning computer, the treatment data defining a radiation therapy treatment to be delivered by a radiation therapy device having independently rotatable X- and Y-collimator jaws in which the X-collimator jaws have a plurality of elements which may be independently moved across a beam axis. A plurality of sets of segment data are generated based on the treatment data. Each of the plurality of sets of segment data include data for positioning the X- and Y-collimator jaws and the plurality of elements in order to deliver a portion of the radiation therapy treatment.
According to some embodiments, ends of opposing elements of the X-collimator jaws may be positioned to abut each other. In some embodiments, the generation of the plurality of sets of segment data further comprises optimizing the plurality of sets of segment data to combine individual ones of the sets of segment data to reduce a total number of the plurality of sets of segment data. In some embodiments, the optimizing includes correcting for a tongue and groove effect in each of the segments. In some embodiments, the optimizing includes generating at least a first set of segment data in which at least one set of opposing elements of the X-jaws are positioned to abut each other.
According to some embodiments, a radiation therapy method is provided which includes establishing a treatment plan; rotating a first and a second radiation blocking device about an axis to produce a portal shape, the second radiation blocking device comprising a pair of jaws independently rotatable of the first radiation blocking device and having a plurality of elements disposed thereon that are individually movable across the axis. A position of at least one of the plurality of elements is adjusted to abut an opposing one of the plurality of elements to adjust said portal shape according to the treatment plan. A radiation beam is directed along the axis toward a treatment zone, the radiation beam shaped by the first and said second radiation blocking devices and the plurality of elements of the second radiation blocking device.
In some embodiments, the plurality of elements each have a top segment, a bottom segment and a tongue and groove segment disposed therebetween, and the segments are selected to minimize beam leakage and beam edge penumbra of the beam. In some embodiments, the plurality of elements are formed to move in an arc across the axis, a shape of the arc selected to maintain an end of each of the elements to match a beam edge divergence from a source of the radiation beam.
In some embodiments, a rotatable multi-element beam shaping device is provided which includes a first assembly, rotatable about a central axis through which a beam passes. The first assembly has a first and a second jaw adapted to move across the central axis to shape the beam. A second assembly, positioned below the first assembly, is also rotatable about the central axis, and has a third and a fourth jaw adapted to move across the central axis to further shape the beam. The first and the second assemblies, according to the invention, are separately controllable. For example, the upper assembly may be rotated about the axis independently of the rotation of the lower assembly about the axis. The result is a beam shaping device which permits the generation of a beam shape which conforms to the shape of a treatment zone on a patient, particularly with reduced penumbra and undulation values for the beam shape.
In one embodiment, beam shaping is further enhanced through the use of multiple, individually controlled elements in the second assembly. Each of the elements may be controlled to individually move across the central axis to shape the beam. In one embodiment, the elements are fitted together using tongue and grooves, and move using bearings located on alternating elements. In one embodiment, the elements are shaped to move in an arc across the axis, maintaining an element end distance from the beam source.
In one embodiment, the position of the first and second assemblies may be manipulated during a treatment to provide a dynamic approach to radiation therapy.
The present invention is not limited to the disclosed preferred embodiments, however, as those skilled in the art can readily adapt the teachings of the present invention to create other embodiments and applications.